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Python Python Collections (Retired) Dictionaries Unpacking Dictionaries

dongji cui
dongji cui
2,464 Points

Questions of if.. in syntax in python

def word_count(a_string):
  string_dict = {}
  for word in a_string.split():
    if word in string_dict:  # can anyone explain code in this line. I am totally confused, because there is nothing in string_dict. How can we use if... in to determine ?
        string_dict[word] += 1
        string_dict[word] = 1
  return string_dict

a_string = "I am what i am because of God"
a_string = a_string.lower()

Hi dongji cui, I've formatted your code to make it easier to read. Also, just note that comments in Python use the hash/pound symbol: #

1 Answer

Hi dongji cui, you're correct, it is checking if the word already exists in string_dict as a key.

The reason it is done this way is because if you try and change the value of a dict key that doesn't exist, you will get a KeyError. This if/else statement checks to make sure it exists and if it doesn't, it will create it.

If it does, it will increase the value by 1 (that is, it will increment the counter value for that word).

If not, it will add the word to string_dict as the key, and make the value equal 1 to indicate the word has appeared once.

It will continue on for each word in the string until it finishes.